1. Field of the Invention
The present invention relates to a hardness tester.
2. Description of Related Art
A hardness tester is known which measures hardness of a sample by pressing an indenter into a surface of the sample to form an indentation and measuring dimensions of the indentation, or by measuring a pressing depth of the indenter when the indentation is formed. In such a hardness tester, before pressing an indenter, confirmation is required as to whether a pressing position (test point of the sample) is positioned directly beneath the indenter. When using a Rockwell harness tester or a Brinell hardness tester for example, a method to confirm visually is known in which the test point is brought closer to the indenter while lifting a vertical stage arranged immediately beneath a pressing mechanism. In addition, when using a Vickers hardness tester, a method is known in which a microscope measuring an indentation length of the tester is used and the test point is aligned to a predetermined position while surveying the entire surface of the sample. However, in the visual confirmation method, a task of bringing the indenter closer to the sample is performed while observing obliquely, rather than from directly above, with respect to a pressing direction. Therefore, the visual confirmation method may cause a positioning drift relative to an expected position and also take time and effort for adjustments. In addition, in the microscope confirmation method, an approximate test position of the sample must first be identified using a low-magnification field lens, and then the test position of the sample needs to be identified by switching to a high-magnification field lens, thus taking time and effort for adjustments. In addition, when using only the high-magnification field lens, it is difficult to identify the test position of the sample due to a narrow field of view.
In contrast, Japanese Patent No. 4750314, for example, proposes a technology to determine with certainty a test point of a sample in one trial. A ring-shaped illumination pattern is formed on a surface of the sample by a plurality of light sources concentrically installed on an indenter column, and the sample is positioned with fine adjustments to allow the test point of the sample to align with a center of the illumination pattern.
However, in the device described in Japanese Patent No. 4750314, the test point of the sample is adjusted so as to align with the center of the illumination pattern by a visual estimation. Therefore the adjusted position may still be offset from the actual test point.